Specific antisera for short and reliable plasma estriol (E3) assays are being produced and tested. Radioimmunoassays (RIA) for plasma total as well as unconjugated estriol are being developed. Concentrations of plasma total and unconjugated E3 will be determined in a large number of women with uncomplicated pregnancies in order to obtain normal values. The presence, extent and possible causes of diurnal variations of plasma E3 concentrations will be analyzed. Plasma total and unconjugated E3 will be measured serially in hospitalized high risk pregnant patients and compared with their 24h urinary E3 excretion and clinical course in order to assess the clinical value of plasma E3 monitoring. Plasma E3 will also be measured prior to and during temporal reductions in uterine blood flow (oxytocin stress test) to explore the feasibility of a dynamic estriol test. Protein binding of E3 and E3 conjugates to plasma protein(s), particularly human serum albumin, is being studied.